Boomerang - Design

Design

A returning boomerang is a rotating wing. Though it is not a requirement that the boomerang be in its traditional shape, it is usually flat. A falling boomerang starts spinning, and most then fall in a spiral. When the boomerang is thrown with high spin, the wings produce lift. Larger boomerangs are used in hunting, thus they drop on the ground after striking the target. Smaller ones are used in sport, and are the only boomerangs that return to the thrower. Because of its rapid spinning, a boomerang flies in a curve rather than a straight line. When thrown correctly, a boomerang returns to its starting point.

Returning boomerangs consist of two or more arms, or wings, connected at an angle. Each wing is shaped as an airfoil.

As the wing rotates and the boomerang moves through the air, this creates airflow over the wings and this creates lift on both "wings". However, during one half of each blade's rotation, it sees a higher airspeed, because the rotation tip-speed and the forward speed add, and when it is in the other half of the rotation, the tip speed subtracts from the forward speed. Thus if thrown nearly upright each blade generates more lift at the top than the bottom.

While it might be expected that this would cause the boomerang to tilt around the axis of travel, because the boomerang has significant angular momentum, gyroscopic effect causes the plane of rotation to tilt about an axis that is 90 degrees to the direction of flight, and this is what curves the flight in such a way that it will tend to return.

Thus gyroscopic precession is what makes the boomerang return to the thrower when thrown correctly. This is also what makes the boomerang fly straight up into the air when thrown incorrectly. With the exception of long-distance boomerangs, they should not be thrown sidearm or like a Frisbee, but rather thrown with the long axis of the wings rotating in an almost-vertical plane. When throwing a returning boomerang correctly, it is important to follow the correct instructions to achieve a successful return.

Fast Catch boomerangs usually have three or more symmetrical wings (in the planform view), whereas a Long Distance boomerang is most often shaped similar to a question mark. Maximum Time Aloft boomerangs mostly have one wing considerably longer than the other. This feature, along with carefully executed bends and twists in the wings help to set up an 'auto-rotation' effect to maximise the boomerang's hover-time in descending from the highest point in its flight.

Some boomerangs have turbulators—bumps or pits on the top surface that act to increase the lift as boundary layer transition activators (to keep attached turbulent flow instead of laminar separation).